1. Field of the Invention
The present invention relates generally to the mechanical mounting of surface mounted components such as connectors to a mounting surface such as a printed circuit board, and more particularly to a fastener arrangement and the method of using this arrangement to mount connectors to printed circuit boards with access to only one side of the printed circuit board thereby facilitating the manufacturing process.
2. Description of the Prior Art
Surface mounted components are typically placed on a printed circuit board and held in place with solder paste until the components are soldered permanently in place with a soldering process such as the reflow process. Until the soldering process is completed, the components held in place with solder paste are subject to moving and falling off the printed circuit board as a result of vibration and shock conditions.
Connectors and connector headers provide the interface between a printed circuit board and other boards or the wires or cables leading to other components. These connectors are typically amongst the largest and heaviest components to be mounted to the board. As was the case for other components, solder paste is typically used initially to hold the connectors in position, and solder helps hold the connectors in place once the soldering process is completed; however, mechanical fastening of these connectors to the printed circuit board is also generally desirable for a number of reasons. For example, these surface mounted connectors typically include contacts which must be spring loaded against the printed circuit board to insure good electrical contact. Mechanical fastening is used to apply the necessary load force. Additional connection strength between connector and board is also required to withstand the forces occurring upon insertion and removal of a mating connector with the board mounted connector, and further necessitates some form of mechanical fastening in addition to the solder connection. In order for a mechanical fastener for connecting a connector to a printed circuit board to be practical, it must be able to withstand the high temperatures associated with the reflow process. These temperatures may typically reach about 450.degree. F. Further, fastening must be performed with very little impact force so that other components mounted with solder paste will not fall off or move. In addition to minimizing manufacturing costs, it is desirable to accomplish the fastening from one side of the board only, the side on which the connector is mounted.
A variety of mechanical fasteners have been used in an attempt to meet the requirements of critical applications such as the one described above. It is commonplace in the prior art to provide connectors and connector headers with plastic posts that are inserted through the printed circuit board and heat staked. There are a number of disadvantages to this fastening technique. One is the requirement for heat stake tooling. Another is the necessity of having access to both sides of the printed circuit board. In addition, a carefully controlled force on the top of the connector must be provided to apply the proper force on the springs of the connector. While heating the plastic posts for purposes of heat staking, it is difficult to carefully control the force on the connector, making it difficult to achieve good contact of the connector to the board. Finally, the above described process is expensive and the connector must be destroyed if the connector needs to be removed, serviced or repaired.
Also commonplace in the prior art is the use of rivets to fasten components to their mounting surface. Various forms of rivets have been used, all of which have significant disadvantages. Rivets generally require access to both sides of the printed circuit board. Specialty rivets such as flair rivets or pop-rivets have the further disadvantage of requiring a high shock force during their application. This shock force can of course have a deleterious effect on the mounting of other components. All the available rivet solutions have the further disadvantage of requiring special tools, allowing poor control of the mounting force, and maintaining poor control of tolerances.
Additional prior art technologies include "snap" action fasteners. These fasteners are typically plastic. They are compressed a they fit through the mounting hole in the mounting surface and spring out at the bottom when the hole is cleared. The critical disadvantage of this technique is the inability of the materials that are presently used from withstanding the required temperatures of such processes as reflow soldering. With snap action fasteners, it is again difficult to control tolerances and to maintain a constant mounting force.
More recent attempts to overcome the problems outlined above still fall short of their goal. A two piece fastener composed of a post with a screw head and a protruded surface is used to spread a mating plastic cylinder mounted through the mounting surface. The screw head is turned using a conventional screwdriver, and, in a quarter turn of the screw head, the protruded surface on the end of the post opposite the screwhead acts to cam apart the portion of the cylindrical shaft below the mounting surface. This technique requires two pieces, has difficulty in withstanding the required temperature range and is relatively expensive.